When you built this system, you did reformat the hard drive and re-install everything from scratch, didn't you?
Also if you believe it to be Video dribers, you can run the system without any nVidia drivers, having removed them (and used Driver Cleaner) - you can simply use the build-in VGA driver.
Sure it will be sluggish... but will enable you to prove (or disprove) that the graphics drivers are the cause.....